This invention relates to an iron core for a three-phase electromagnetic induction machine.
The saving of energy and resources has been recently advocated resulting in improvements in iron cores for a three-phase electromagnetic induction machine. A conventional iron core of the type referred to has comprised a pair of outer legs, a central leg, a pair of first yokes for connecting one end of the central leg to corresponding ends of the outer legs and a pair of second yokes for connecting the other end of the central leg to corresponding ends of the outer legs. In order to manufacture such an iron core, electrical steel sheets have been cut into strips extending in the rolled direction thereof and having a width equal to the common width of the legs and yokes. Each of the strips has been cut into laminations having respective shapes specified to the legs and yokes. Thus, each of the laminations has a magnetization direction coinciding with the longitudinal axis thereof. The laminations have been stacked on one another and abutted against associated ones of the laminations to form the legs and yokes interconnected as described above. At that time, the connection of the outer leg to each of the first and second yokes has included the stacked laminations of the outer leg connected to those of the first or second yoke through angle butt joints and also lapped in alternating manner on the laminations of the first yokes adjacent thereto. These laminations have been cut from the electrical steel sheets without any scrap but a magnetic flux flowing through each lamination has been locally concentrated on that portion of the overlaid or underlaid lamination located at the mating joint resulting in an increase in iron core loss.
In order to reduce this increase in iron core loss, another iron core for a three-phase electromagnetic induction machine has been proposed. The proposed iron core has been different from the first mentioned iron core in the manner in which the laminations of the outer leg are connected to those of each of the first and second yokes and the shape of the laminations forming the central leg. More specifically, the laminations of the outer leg have been connected to those of the first or second yoke through angle butt joints arranged in stepped manner with equal incremental intervals. Thus, the local concentration of the magnetic flux has been alleviated. However, since the central leg has been formed of a stack of hexagonal laminations, scraps have occurred upon cutting strips of electrical steel sheets into laminations. This is because the laminations of the central leg change their shape from the parallelogram in the firstmentioned iron core to the hexagon in the proposed iron core and the laminations forming the yokes change in shape accordingly. Further a waveform of a magnetic flux flowing through each of the outer legs has been much distorted as compared with the first mentioned iron core including the central leg formed of a stack of parallelogramic laminations.
Accordingly, it is an object of the present invention to provide a new and improved iron core for a three-phase electromagnetic induction machine reduced in iron core loss and formed of stacked laminations cut from an electrical sheet without any scrap.